This invention relates in general to lifts for lifting and transporting patients. More particularly, the invention relates to a load sensing safety device for patient lifts and more particularly for vertical lifts.
Lifts for lifting and transporting patients are well known. Such lifts typically include a base that is usually supported for movement relative to a supporting surface, such as a floor. Extending upwardly from the base is a mast and extending forward from the mast is a boom. From a forward end of the boom is suspended a rigging of some sort, such as a sling hanger for supporting a sling, which in turn is provided for supporting the patient. The boom is displaceable to vertically move the rigging to raise and lower a patient supported by the rigging. With the patient supported by the rigging, the lift may merely support the patient in a fixed position, or the lift may be moved relative to the supporting surface to transport the patient.
There are two common ways in which the boom is typically displaced. In one manner, the boom is supported for pivotal movement relative to the mast and an actuator is angularly disposed between the mast and the boom. Extending the actuator causes a free end of the boom to be raised and contracting the actuator causes a free end of the boom to be lowered. In another manner, the boom is supported for vertical movement relative to the mast. An actuator causes the entire boom to be raised and lowered. The actuator often includes a flexible belt for providing a lifting force for raising and lowering the boom.
The boom and patient support rigging are often very heavy. If the patient should come into contact with an underlying obstruction and the actuator continues to lower the boom, the weight of these components can be applied against the patient, resulting in patient injury. When the lift employs a flexible belt to transmit lifting force, further potential for injury exists if a patient encounters an underlying obstruction because the belt may continue to be extended and accumulate as slack. If the obstruction is suddenly removed, the patient may move abruptly downward until the slack of belt is taken up.